Very common newbie mistake: the phrase "appears to be" implies that it isn't what it seems. Since it is a taxidermied lion, this phrase is not necessary.

All subjects when they first see SCP-XXXX demonstrate signs of fear and anxiety.

Wording is wonky here. It should probably be along the lines of:

When a subject firsts views SCP-XXXX, they begin to demonstrate signs of fear and anxiety.

Its tags show it was shot in 12-06-██64, however it shows no signs of aging.

"Tags attached to SCP-XXXX…" instead of "Its tags…" A bit too casual.

"…showed that it was killed…" instead of "…show it was shot…"

According to victims they hear 'whispers' coming from SCP- XXXX.

"test subjects" instead of "victims". This seems to me at least be less casual. I would also recommend this change for each instance of "victims"

Place a comma after "victims". It is an introductory phrase.

They claim that something lures them in and they become curious to hear what the whispers are saying.

I would probably re-write this to go along the lines of this:

These whispers begin to lure in subjects, with the intent of investigating where this sound is originating from.

Less causal overall.

While I'm here, this article has a lot of instances of casual wording/sentence structure. Seeing as you're writing a pseudo-scientific document, it's probably for the best to comb through the article to iron out these instances.

Research as to where the whispers are coming from are on a pause.

Why? The Foundation is a research facility, so it makes no sense to stop it completely stop researching this certain aspect without a good reason.

they will begin to feel some kind of force, making it harder for them to turn away, their curiosity growing stronger.

How does The Foundation know the subject's curiosity is growing stronger? For all they know, they could be brain dead. Otherwise, I would remove that little detail at the end.

After approximately 5 minutes of just standing in front of SCP-XXXX now in some kind of trance, it will slowly start to become animate and stand up.

The first half of the sentence doesn't make sense writing-wise (I understand what you're trying to say, but you should clean it up). Also, say "SCP-XXXX" instead of "it"

It has also been noted that SCP-XXXX will change pose from time to time.

Not sure why you attached this at the end. It really doesn't add anything to the article.

The idea isn't bad by any means, but the biggest problem is that you really don't do much with it. For me at least, it isn't about the idea as much as what you can do with it.

When you look at Series III and Series IV articles, you can see that all of them are essentially stories written in a limited format. Just writing about the creature/object itself really won't get you anywhere, and it certainly won't get you praise from a lot of other site members.

From me, I would recommend sitting down and thinking about what kinds of stories you could make with this skip. Once you've settled with an idea, incoperate it into your article. A good story can turn a meh or subpar article into a very good article.

Of course, this is just my critiques: others will have more stuff to talk about.

SCP-XXXX is to be contained in a standard 5x5m containment chamber on a pedestal.

Specifying that it needs to be on a pedestal seems kind of weird to me — the general rule of thumb is, containment procedures only say what needs to be done to prevent a breach. If the pedestal doesn't need to be there, you can just say "standard 5x5m containment chamber" or even "standard large object containment locker" (5x5m seems like kind of a big room to dedicate to a piece of taxidermy you're basically just storing).

Nobody is to 'pet' or touch SCP-XXXX and if so happens, they will be declared dead.

Suggestion — "Personnel interacting with SCP-X are required to wear full-body protective gear. Physical contact with SCP-X has been fatal in 100% of recorded incidents."

SCP-XXXX is a taxidermied mountain lion.

I looked it up, and taxidermied isn't a word. Maybe "SCP-X is the body of a mountain lion, preserved through taxidermy and mounted in a 'hunting/resting/whatever you want' pose?"

Tags attached to SCP-XXXX shows that it was killed in 12-06-██64, however it shows no signs of aging.

Tags attached where? It seems worth specifying if they're in its ear or around its neck or something; the first thing that comes to mind for me would actually be "a plaque on SCP-X's mount states that it was killed in 12-06-xx64" (by the way, why is the year censored? why would the Foundation keep that information a secret from its own staff? I don't think it adds anything. It might actually up the creep factor a little bit if you pick a year that doesn't really make sense, like 1364 or 1464). "it shows no signs of aging" feels off; you could say "the exterior of SCP-X shows no signs of wear," though I'm not sure either of these details are necessary at all.

When a subject firsts views SCP-XXXX, they begin to demonstrate signs of fear and anxiety.

I like this, but it can become a slippery slope toward cliche compulsion effects, which we want to avoid. This is decent clinical tone, but it would be better if it specified what signs they demonstrate, even if it's just "individuals viewing SCP-X consistently report feeling fear and anxiety."

According to test subjects, they hear 'whispers' coming from SCP- XXXX. These whispers begin to lure in subjects, with the intent of investigating where this sound is originating from. Test subjects describe a nervous fascination and a desire to move closer. This can be resisted with effort, especially if the subject is aware of SCP-XXXX's anomalous properties.

This will get you flak for being a cliche compulsion effect. There's a whole guide on compulsive SCPs somewhere — the gist of it is that it's lazy storytelling, because it's basically saying "people go investigate because they just do." I think we can avoid that with a couple of changes.

What if, instead of compelling you to go find the lion, the whispers just really confuse and disorient you? You could say something like "over 90% of subjects compare the experience to dreaming" or say that they become unable to navigate their environment. I like the idea of people feeling like they're lost in a maze — they're not compelled to seek out the statue, they just end up there because they're so confused. Describing that well would be a challenge, but I think it's the key to making this not just another X-that-makes-you-do-Y.

Survivors have reported that if subject is within 2 meters of SCP-XXXX they will begin to feel some kind of force, making it harder for them to turn away, their curiosity growing stronger. After approximately 5 minutes of just standing in front of SCP-XXXX now in some kind of trance, SCP-XXXX will slowly start to become animate and stand up.

Clinical tone is off in this paragraph; even if it's just by putting the "hard to turn away" and "curiosity" into quotes, you need to describe it in terms of what we can see and hear and measure, not things that the victim is feeling. Same when you say "now in some kind of trance"; you could say something like "subjects become non-responsive," but we as scientists can't assume the subject is in a trance (as opposed to, for example, suddenly being uncooperative, or listening to something we can't hear) unless they say so themselves or we ask them something and they don't answer.

More importantly, it's still just a stock compulsive effect. I like the vibe of what you're trying to do, but I think you can put it in more precise tone and add some depth to it at the same time by making it more subtle. I like the idea of the subject starting to become more curious about lions, or even start talking about living forever, or voices from a place without people. At this point, I think the best presentation is actually an interview/experiment type log where they put a tether on someone so they can yank them back, and interview them as they approach it. The person can start describing being in a misty/dark maze as they wander around, even though they haven't really gone that far, and they start talking their weird stuff as they meander toward the lion.

When they get to it, I like the idea of standing in awe (maybe they won't respond to the questions anymore, they're just staring at it for a few minutes). Then, what if instead of the lion moving, the person just says that it is? They're seeing it move, but the observers just see them keep standing there until they turn into taxidermy.

SCP-XXXX will jump down from the pedestal and begin to circle the subjects legs, rubbing itself against them much like a housecat. At this point the subject will be dead and unmoving, frozen in a pose, creating SCP-XXXX-1. SCP-XXXX will then back away and stare up at SCP-XXXX-1, nodding a bit as if approving. After this has been done SCP-XXXX will leap back up onto the pedestal and become inanimate once more.

This was actually the image that got me interested in this. It's really spooky. I think the way to make this work is to have it in an experiment log, as mentioned above. some poor d-class can describe it rubbing him like a housecat and licking his hand, and maybe say something that ties into whatever he was talking about as he approached it, and then he turns into taxidermy. All the researchers see is him standing there until he freezes and stops talking, and when they do an autopsy they find wire and stuffing typical of the taxidermy process.

When sent in to retrieve SCP-XXXX-1 it has been noted that they are now works of taxidermy, their eyes replaced with glass eyes. SCP-XXXX-1 will not rot and are perfectly preserved. They do not become animate. It is still unknown how SCP-XXXX does this.

As above, I think you should cut this, and just end on the experiment log — "wire and stuffing typical of the taxidermy process" actually seems like a chilling end line, or something similar to that.

It's still kind of a simple concept, but I think the execution can make this work without having to add a whole backstory or anything. If you can put everything into measurable scientific terms while expanding a little on the dreamlike atmosphere, you'll be on the right track. Hope this helps!